Many gastropod species follow their own mucous trails and the trails of other species. Demonstrated functions for the behaviour include: 1) mate-finding, 2) food-finding, and 3) reducing energy expended in crawling. Apart from recognising that a trail exists to be followed, individuals of many species have the ability to distinguish polarity in the trail’s chemistry and thus can follow it in one direction or the other. Some species can also determine sex and nutritional status of an individual laying down the tral. Studies on trail-following in the Eastern mud snail Ilyanassa obsoleta show that tracking fidelity is about 80% for trail shapes shown here. A tracking snail will deviate less than 15-cm width beyond the margin of the trail. A tracking Ilyanassa turns onto a trail in the direction it is laid about 85% of the time and this happens whether the trail is on glass or on a skim of marsh mud. Possible explanations for this, but not tested in this particular study, include recognition in the trail of: 1) chemicals secreted in a certain sequence, 2) change in surface structure of the mucus, 3) difference in frictional resistance, and 4) chemical gradient. Additionally, a tracking individual will preferentially follow another snail’s trail over its own trail. The authors speculate that this behaviour may be involved in migrations of Ilyanassa to subtidal areas to form aggregations in winter. Trott & Dimock 1978 Mar Behav Physiol 5: 91.

NOTE the studies described here are actually done in North Carolina and Masachusetts; however, mud snails Ilyanassa obsoleta were brought to the west coast in shipments of oysters Crassostrea virginica 60-100 years ago and have since become well established in many mudflat areas. Apart from performing a vital role in consuming detritus, not just from seaweed and leaf degradation, but also from sewage-treatment plants, Ilyanassa is known to host a schistozome flatworm species Austrobilharzia variglandis that causes swimmer’s itch

NOTE by appropriate tilting of the glass tracking surface, the researchers use the natural positive geotaxis of Ilyanassa to form the alpha- and sigma-shaped tracks shown here